Apparatus and method for transferring heat

ABSTRACT

An apparatus is for transferring heat. The apparatus has a heat transfer circuit with a heat transfer medium. The heat transfer circuit has: a heat receipt path having a first heat exchanger; a heat dispatch path having a compressor device and a second heat exchanger; and an intermediate path having an ejector device and a separator. A primary first heat exchanger is arranged: a) in a primary heat receipt path in the heat receipt path and connected to the separator; or b) in the separator. A secondary heat receipt path is arranged with a secondary first heat exchanger connected to the suction inlet of the ejector device. A method is for transferring heat using the apparatus.

INTRODUCTION

The invention relates to an apparatus and a method for transferring heatcomprising a heat transfer circuit with a heat transfer medium. The heattransfer circuit comprises a heat receipt path comprising a first heatexchanger for transferring heat to the heat transfer medium, a heatdispatch path comprising a compressor device and a second heat exchangerfor transferring heat away from the heat transfer medium; and anintermediate path between the receipt path and the dispatch path. Theintermediate path comprises an ejector device and a separator. Theejector device comprises a main inlet connected to the dispatch path, asuction inlet, and main outlet connected to the separator. The separatoris configured to receive heat transfer medium from the ejector deviceand to provide heat transfer medium to the receipt and dispatch paths.

PRIOR ART

Cooling, i.e. the transfer of heat from one location to another, isrequired in a vast range of applications, for example for chillers andair conditioning of buildings and for cooling refrigerators andfreezers. A common cooling method relies on vapour-compressionrefrigeration cycle, wherein a heat transfer medium, typically called arefrigerant, changes phase during the refrigeration cycle. A basicvapour-compression refrigeration system typically comprises acompressor, wherein the heat transfer medium in the gaseous phase iscompressed into a superheated gaseous phase. This superheated gaseousphase then enters a condenser, wherein the superheat is transferred awayfrom the heat transfer medium, and the gaseous heat transfer medium iscondensed into a liquid. This liquid then passes a flow restriction,e.g. an expansion valve, wherein the pressure decreases such that a partof the liquid vaporises and thus cools down. This now cooled mixture ofgaseous and liquid heat transfer medium subsequently enters anevaporator, wherein the remaining portion of the heat transfer medium inliquid phase vaporises by transferring heat to the heat transfer mediumfrom the system which should be cooled, e.g. a refrigerator. The gaseousheat transfer medium then enters the compressor again for the cycle torestart.

The choice of heat transfer medium is important for the performance ofthe refrigeration system. A typically used heat transfer medium isFreon, which comprises haloalkanes. As haloalkanes may contribute to thedepletion of the ozone layer, other alternatives which reduce the ozonedepletion are being used in newer cooling systems, for examplehydrofluorocarbons and hydrochlorofluorocarbons. However, theserefrigerants all have a large global warming potential, so refrigerantswhich are better for the environment are being investigated.

A possible substitute for the refrigerants used today is carbon dioxide,which is nontoxic, cheap, has a low global warming potential, and may bea suitable refrigerant for most applications. On the downside carbondioxide needs a relatively high pressure and has a low criticaltemperature of around 31° C., which may cause difficulties in warmerclimates. Additionally, the cycle loses a large degree of energy due toirreversibility in the carbon dioxide expansion process when it goesfrom a supercritical region to the two-phase region.

To make use of some of the energy lost in the carbon dioxide expansionprocess, it has been proposed to include an ejector in thevapour-expansion refrigeration cycle after the condenser/gas cooler. Anejector is a device which comprises a main inlet, a main outlet, and asuction inlet, and which is constructed in such a way that a suctionpressure is created in the suction inlet when a flow into the main inletis established. The heat transfer medium from the main inlet and thesuction inlet is mixed inside the ejector. A gas-liquid separator isalso included after the ejector. The separator separates the heattransfer medium into gaseous carbon dioxide, which enters the compressorand starts a new cycle, and liquid carbon dioxide, which goes throughthe expansion valve and the evaporator as described above, beforeentering the ejector suction inlet. A diagram of this prior artejector-expansion cycle is shown in FIG. 1. The overall effect of theprocess is to decrease the energy needed for the compressor compared tothe cycle without the ejector, as some of the energy lost in theexpansion process is used to drive the refrigeration cycle. This processworks well at high cooling need, however, at low cooling need the systemwill have difficulties cooling since the ejector requires a minimum flowthrough the main inlet to create a suction pressure in the suctioninlet. It will therefore be difficult to regulate the cooling, the heatexchange will be unsteady, and the energy efficiency will decrease.Additionally, the system may risk a situation where the heat transfermedium in the separator becomes very cold and boils at low pressure andtemperature, whereby the compressor cannot run as intended due to toolow suction pressure. Thereby, no or insufficient flow will reach theejector inlet to create a suction pressure at the suction inlet, so noheated heat transfer medium will pass from the evaporator to theseparator to heat up the heat transfer medium in the separator. Thissituation may be referred to as a dead lock position.

“Transcritical CO₂ Refrigeration Cycle with Ejector-Expansion Device”,International Journal of Refrigeration, Volume 28, Issue 5, August 2005,Pages 766-773, Daqing Li, Eckhard A. Groll, discloses an apparatus and amethod for transferring heat according to FIG. 1.

EP1327838A2, WO2012012488A1, US2004003608A1, and CN104359246A discloseother prior art devices for transferring heat.

SUMMARY OF THE INVENTION

The invention has for its object to remedy or to reduce at least one ofthe drawbacks of the prior art, or at least provide a useful alternativeto prior art. The object is achieved through features which arespecified in the description below and in the claims that follow. Theinvention is defined by the independent patent claims, and the dependentclaims define advantageous embodiments of the invention.

In particular, a first object of the invention is to provide anapparatus for transferring heat with improved efficiency at high heattransfer requirement. A second object of the invention is to provide anapparatus for transferring heat with improved stability at low heattransfer requirement. A third object of the invention is to provide anapparatus for transferring heat with reduced risk of going into a deadlock position. A fourth object of the invention is to provide the aboveimprovements for an apparatus that is based on a heat exchange mediummainly comprising CO₂.

The above objects are achieved by means of an apparatus for transferringheat. The apparatus comprises a heat transfer circuit with a heattransfer medium, wherein the heat transfer circuit comprises: a heatreceipt path comprising a first heat exchanger for transferring heat tothe heat transfer medium; a heat dispatch path comprising a compressordevice and a second heat exchanger for transferring heat away from theheat transfer medium; and an intermediate path between the receipt pathand the dispatch path, which intermediate path comprises an ejectordevice and a separator, wherein the ejector device comprises a maininlet connected to the dispatch path, a suction inlet, and main outletconnected to the separator, and wherein the separator is configured toreceive heat transfer medium from the ejector device and to provide heattransfer medium to the receipt and dispatch path.

The first heat exchanger comprises a primary first heat exchanger and asecondary first heat exchanger, and the apparatus is characterised inthat: a) the heat receipt path further comprises a primary heat receiptpath arranged with the primary first heat exchanger and connected to theseparator without passing the ejector device; or b) the primary firstheat exchanger is arranged in or in direct connection to the separator,wherein for both options a) and b) the heat receipt path furthercomprises a secondary heat receipt path arranged with the secondaryfirst heat exchanger connected to the suction inlet of the ejectordevice, wherein the secondary heat receipt path further comprises anexpansion device upstream of the secondary first heat exchanger. In analternative embodiment, the heat receipt path may comprise both aprimary heat receipt path arranged with the primary first heat exchangerand connected to the separator without passing the ejector device; and aprimary first heat exchanger arranged in or in direct connection to theseparator.

The effect of the apparatus is to transfer heat to the heat transfermedium at the first heat exchanger, and transfer heat away from the heattransfer medium at the second heat exchanger. The first heat exchangerand the second are separated from each other. The apparatus may cool orheat a space, for example for use as a water chiller unit orrefrigerator or air condition in a house.

The heat transfer medium is conducted in the circuit by the compressordevice. Typically, the compressor device may be a compressor which maycompress the gaseous heat transfer medium, whereby the temperature ofthe gaseous heat transfer medium will increase. The heat transfermedium, which may at this stage be a superheated vapour, then enters thesecond heat exchanger, such as a gas cooler or a condenser, wherein heatwill be transferred away from the heat transfer medium. The heattransfer medium will thereby cool down, and potentially condense fullyor partially into a liquid. After the second heat exchanger, the heattransfer medium continues into the main inlet of the ejector device,where the heat transfer medium at least partially expands. If the flowthrough the ejector device is sufficiently high, a suction pressure maybe created at the ejector suction inlet upon expansion of the heattransfer medium in the ejector.

The term “ejector device” shall be understood as a pump-like device thatcreates a suction at the suction inlet. The ejector device is alsodenoted ejector or injector. The suction is due to the internal shape ofthe ejector device.

After passing through the ejector device, the heat transfer medium,typically existing as a mixture of gaseous and liquid heat transfermedium, enters the separator, where the heat transfer medium isseparated into a gaseous phase and liquid phase. The separator may forexample be an accumulation tank, wherein the liquid may separate at thebottom due to gravity. From the separator, the heat transfer medium,typically as a liquid, is conducted to the heat receipt path and thefirst heat exchanger for transferring heat to the heat transfer medium.The first heat exchanger comprises the primary first heat exchanger andthe secondary first heat exchanger, which for example are evaporators.

When the heat transfer medium reaches the primary first heat exchanger,either in the separator or in the primary heat receipt path, heat willbe transferred to the heat transfer medium. If the primary first heatexchanger is in the primary heat receipt path and the heat transfermedium is in liquid form at this stage, it may at least partiallyvaporise into a gaseous phase, or typically a mixture of liquid andgaseous heat transfer medium. Optionally, more than one primary firstheat exchanger may be connected in series in the primary heat receiptpath, whereby more, or all, of the liquid may vaporise. The mixture maythereafter be returned to the separator without passing the ejectordevice. The term “without passing the ejector device” shall beunderstood as the heat transfer medium from the primary first heatexchanger being conducted to the separator without being acted upon bythe ejector device. If the primary first heat exchanger is positioned inor in direct connection to the separator, heat may be transferreddirectly to the heat transfer medium in the separator, possible causingsome of the heat transfer medium in the liquid state to vaporise into agaseous phase.

In the secondary heat receipt path, the heat transfer medium, typicallyas a liquid, pass the expansion device, such as an expansion valve, acapillary tube, or another kind of pressure restriction, where it mayexpand at least partially into a mixture of gaseous and liquid heattransfer medium.

Upon expansion, the temperature of the heat transfer medium willdecrease. The heat transfer medium then enters the secondary first heatexchanger, wherein heat will be transferred to the heat transfer medium.

The expansion device is arranged upstream of the secondary first heatexchanger. The term “upstream of the secondary first heat exchanger”relates to the fact that the expansion device receives the heat transfermedium in the secondary heat receipt path prior to the secondary firstheat exchanger.

Due to the expansion device the heat transfer medium will have a lowertemperature at the secondary first heat exchanger than at the primaryfirst heat exchanger. Accordingly, the primary first heat exchanger andthe secondary first heat exchanger handle separate portions oftransferring heat to the heat transfer medium in the heat receipt path.

The flow of the heat transfer medium in the secondary heat receipt pathis caused by the suction pressure at the suction inlet of the ejector.The heat transfer medium from the secondary heat receipt path willtherefor pass through the suction inlet of the ejector and out of theejector outlet into the separator. From the separator, the heat transfermedium, typically in gaseous phase, is then passing to the compressordevice for the next cycle.

By including a primary first heat exchanger directly in the separator orin a primary heat receipt path which bypasses the ejector, and thesecondary first heat exchanger in a secondary heat receipt path whichpasses the ejector, the problem with the unsteady cooling at low coolingrequirement, which is present without primary first heat exchangerpositioned in the primary heat receipt path or in or direct connectionto the separator, will be avoided. At low cooling requirement thecompressor device will run at reduced capacity, and the ejector devicewill not have sufficient flow through the main inlet to create a suctionpressure at the suction inlet. The ejector device will thereforesubstantially not cause any heat transfer medium to flow through thesecondary heat receipt path. However, the heat transfer medium may stillreceive heat at the primary first heat exchanger if this is positionedin the separator or in the primary heat receipt path. The apparatus willtherefore provide more stable heat transfer at low heat transfer needand more effective heat transfer at high heat transfer requirement thanprior art apparatuses are capable of. Additionally, the risk of goinginto a dead lock position as described above is eliminated. If theprimary first heat exchanger is positioned in or in direct connection tothe separator, the heat transfer medium in the separator may receiveheat directly from the primary first heat exchanger even if no heattransfer medium is flowing through the secondary heat receipt path. Ifthe primary first heat exchanger is positioned in the primary heatreceipt path, heated heat transfer medium from the primary first heatexchanger may enter the separator also if the flow through the ejectordevice is insufficient to create a suction pressure at the suction inletof the ejector device. Therefore, a primary first heat exchangerpositioned in or in direct connection to the separator, or in theprimary heat receipt path, will both provide a more stable heat transferat low heat transfer need and therefore avoid the risk of going into adead lock position.

According to an embodiment of the invention, the primary first heatexchanger and the secondary first heat exchanger are configured toreceive a further heat transfer medium for transferring heat to the heattransfer medium.

The heat from the further heat transfer medium is transferred to theheat transfer medium in the heat receipt path by means of the primaryfirst heat exchanger and secondary first heat exchanger. By means ofthis configuration of the primary and secondary first heat exchangers itis possible to cool two separate further heat transfer mediums atdifferent temperatures, or one further heat transfer medium in two stepsby leading the fluid past the primary and secondary first heat exchangerin series. In this way the further heat transfer medium will be cooledpartially at the primary first heat exchanger and partially at thesecondary first heat exchanger.

The further heat transfer medium may for example be a liquid, or it mayalternatively be hot air or gas which is passed across the surfaces ofthe primary and secondary first heat exchangers in series. In this waythe hot air or gas may be partially cooled at the primary first heatexchanger and further cooled at the secondary first heat exchanger. Thefurther heat transfer medium is for example water.

The flow of the heat transfer medium in the secondary heat receipt pathmay be caused by the suction pressure at the suction inlet of theejector. The heat transfer medium from the secondary heat receipt pathwill therefor pass through the suction inlet of the ejector device andout of the ejector outlet into the separator. From the separator, theheat transfer medium, typically in the gaseous phase, may be passed tothe compressor device for the next cycle.

According to an embodiment of the invention, the heat transfer mediummainly comprises CO₂, which is better for the environment than mostother suitable heat transfer mediums. The apparatus may also beparticularly beneficial if the heat transfer medium is CO₂, since itavoids or decreases some of the drawbacks experienced with using CO₂ asthe heat transfer medium in prior art apparatuses. Preferably, the heattransfer medium consists of CO₂, and possible impurities.

According to an embodiment of the invention, the apparatus comprises atleast one sensor for identifying a physical quantity dependent on astate of the heat transfer medium and a control unit, wherein the atleast one sensor is positioned downstream of the secondary first heatexchanger and upstream of the suction inlet of the ejector device, andthe control unit is adapted to receive information from the at least onesensor and control the expansion device on the basis of said informationso that the heat transfer medium is mainly in the gaseous state afterpassing the secondary first heat exchanger.

The control unit controls the flow of the heat transfer medium throughthe secondary first heat exchanger by means of controlling the expansiondevice based on the information from the sensor or sensors so as toensure that all the liquid or essentially all liquid of the heattransfer medium is evaporated in the secondary first heat exchanger,such that only gaseous heat transfer medium enters the suction inlet ofthe ejector device, as the ejector device is configured for accepting agaseous heat transfer medium at the suction inlet. Liquid at the suctioninlet of the ejector device may potentially cause problems. The sensormay for example be a temperature sensor, a pressure sensor, an opticalsensor, or a combination, as the state of the heat transfer medium maybe reliably determined by these properties.

According to an embodiment of the invention, the primary first heatexchanger is positioned in the primary heat receipt path and lower inelevation than the separator, whereby gravity may cause the liquid heattransfer medium in the separator to be led into the primary first heatexchanger. This will assure flow of the heat transfer medium through theprimary first heat exchanger without any additional pump. Alternatively,a pump device may be used.

According to an embodiment of the invention, the heat dispatch pathcomprises an internal heat exchanger for exchanging heat between theheat transfer medium flowing upstream of the compressor device anddownstream of the second heat exchanger. This may increase theefficiency of the apparatus, as there may typically remain a differencein temperature of the heat transfer medium downstream of the second heatexchanger and upstream of the compressor device. The internal heatexchanger may therefore cause heat to be transferred from the heattransfer medium flowing downstream of the second heat exchanger to theheat transfer medium flowing upstream of the compressor device. At thisposition a high temperature may be beneficial, as it may decrease thework needed to be performed by the compressor device to raise thepressure sufficiently. It will also prevent that the compressor willoperate with at a non-optimal low temperature at the inlet of thecompressor.

According to an embodiment of the invention, the apparatus mayfurthermore comprise at least one additional path connecting the heatreceipt path downstream of the separator and upstream of the first heatexchanger to the heat dispatch path downstream of the separator andupstream of the compressor device, wherein the additional path comprisesa flow restriction, e.g. an expansion device. This additional path andflow restriction may be particularly beneficial if the compressor deviceis lubricated by lubricating oil, since the compressor device may inthat situation typically let out a small amount of lubricating oilthrough the outlet of the compressor device, and the lubricating oil maythereby end up in the separator in the liquid phase of the heat transfermedium. By including the additional path with a flow restriction, asmall amount of liquid heat transfer medium including oil maycontinuously be led to the heat dispatch path upstream of the compressordevice. The heat transfer medium may vaporise through the flowrestriction while the lubricating oil will run into the compressor. Aninternal heat exchanger as described above may be included to ensurethat all heat transfer medium is vaporised before the compressor device.

The above objects are furthermore achieved by means of a method fortransferring heat by means of an apparatus according to any of theclaims 1-8. The method comprises the steps of:

-   -   receiving information from at least one sensor for identifying a        state of the heat transfer medium downstream of the secondary        first heat exchanger and upstream of the suction inlet of the        ejector device, and    -   adjusting the flow of the heat transfer medium through the        expansion device on the basis of the information from the at        least one sensor so that the heat transfer medium is mainly in        the gaseous state after passing the secondary first heat        exchanger.

Preferably, the flow of the heat transfer medium is adjusted so thatmore than 90% of the heat transfer medium is in the gaseous state, morepreferably more than 95% of the heat transfer medium.

The above objects are furthermore achieved by means of use of anapparatus according to any of the claims 1-8.

BRIEF DESCRIPTION OF DRAWINGS

In the following is described an example of a preferred embodimentillustrated in the accompanying drawings, wherein:

FIG. 1 shows a diagram of a heat transfer circuit of an apparatus fortransferring heat according to prior art;

FIG. 2 shows a diagram of a heat transfer circuit of an apparatus fortransferring heat according to an embodiment of the invention;

FIG. 3 shows a diagram of a heat transfer circuit of the apparatusaccording to a further embodiment of the invention; and

FIG. 4 shows a diagram of a heat transfer circuit of an apparatus fortransferring heat according to an even further embodiment of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

In the drawings, the reference numeral 10 indicates a heat transfercircuit comprising a heat transfer medium. Identical reference numeralsindicate identical or similar features in the drawings. The drawings arepresented in a simplified and schematic manner, and the features thereinare not necessarily drawn to scale. The short arrows adjacent andparallel to the lines in the diagrams indicate the flow direction of theheat transfer medium in the circuit.

FIG. 1 shows a heat transfer circuit 10 comprising a heat transfermedium according to prior art. The heat transfer circuit 10 comprises aheat receipt path 11, which comprises a first heat exchanger 6 fortransferring heat to the medium, and a heat dispatch path 12, whichcomprises a second heat exchanger 2 for transferring heat away from themedium. Furthermore, the heat transfer circuit 10 comprises anintermediate path 13 between the heat receipt path 11 and heat dispatchpath 12, which intermediate path 13 comprises an ejector device 3 and aseparator 4. In the heat transfer circuit 10, the compressor 1compresses the heat transfer medium (present in a gaseous state),whereby the temperature increases. Upon entering the second heatexchanger 2, for example a condenser, the gas cools down and condensesat least partially into a liquid. The heat transfer medium continuesthrough the main inlet 31 of the ejector device 3, thereby creating asuction pressure at the suction inlet 32, before leaving the ejector 3through the main outlet 33 and entering the separator 4. In theseparator 4, the heat transfer medium is separated into a gaseous phase41 and a liquid 42. From the separator, the heat transfer medium in theliquid state is then passed through an expansion device 5, for examplean expansion valve, wherein it expands at least partially into a vapour,and thereby cools further down. The heat transfer medium, typicallypresent as a vapour-liquid mixture, then enters the first heat exchanger6, wherein heat is transferred to the heat transfer medium, e.g. from afurther heat transfer medium in an external circuit 14. The further heattransfer medium is for example water.

The heat transferred to the heat transfer medium may cause the remainingheat transfer medium in the liquid phase to vaporise. Thereby onlyvapour will continue to the suction inlet 32 of the ejector 3. Also,from the separator, the heat transfer medium in the gaseous phase ispassed to the compressor 1 for the cycle to continue. This prior artcircuit has the problem that at low cooling need the compressor 1 willrun at low power, whereby the pressure at the main inlet 31 of theejector 3 may be too low to cause a suction pressure at the suctioninlet 32 of said ejector 3. This circuit will therefore result inunsteady cooling since the compressor 1 will have to run at high powerfor shorter intervals at low cooling need, which will furthermore beinefficient.

FIG. 2 shows a diagram of a heat transfer circuit 10 of an apparatus 50for transferring heat according to an embodiment of the invention.Compared to prior art, the heat receipt path 11 comprises a primary heatreceipt path 11 a comprising a primary first heat exchanger 7, and asecondary heat receipt path 11 b comprising a secondary first heatexchanger 6 and a controllable expansion device 5, e.g. an expansionvalve. The primary heat exchange path 11 a receives liquid heat transfermedium from the separator 4 and returns a mixture of liquid and gaseousheat transfer medium to the same separator 4 without passing the ejector3. The secondary heat receipt path 11 b receives liquid heat transfermedium from the separator 4 and provides gaseous heat transfer medium tothe suction inlet 32 of the ejector 3.

Thus, at low cooling need when the compressor 1 runs at low capacity,the heat transfer medium will still run through the primary heat receiptpath 11 a, whereby heat will be transferred to the heat transfer mediumthrough the primary first heat exchanger 7, since the primary heatreceipt path 11 a is not connected to the suction inlet 32 of theejector 3. The heat transfer circuit 10 of the invention thus avoids theproblems with the prior art embodiment which may arise at low coolingrequirement. When the cooling requirement increases and the compressor 1runs with higher capacity, a suction pressure at the suction inlet 32 ofthe ejector 3 is established, thus ensuring flow of the heat transfermedium through the secondary receipt path 11 b.

Upon expansion of the heat transfer medium through the expansion device5, the temperature of the heat transfer medium will decrease. Thesecondary first heat exchanger 6 will therefore be able to cool thefurther heat transfer medium in the external circuit 14 to a lowertemperature than the primary first heat exchanger 7.

The apparatus 50 further comprises a control unit 60 and at least onesensor 62 for measuring a physical quantity dependent on a state of theheat transfer medium. The at least one sensor 62 is positioneddownstream of the secondary first heat exchanger 6 and upstream of thesuction inlet 32 of the ejector device 3.

The control unit 60 is connected to the at least one sensor 62 and isadapted to receive information from the at least one sensor 62. Thecontrol unit 60 comprises a logic unit 70 and a memory unit 72. Thereceived information from the at least one sensor 62 is adapted to bestored in the memory unit 72. The logic unit 70 is configured to processthe stored information from the sensor 62 and determining the state ofthe heat transfer medium downstream of the secondary first heatexchanger 6 and upstream of the suction inlet 32 of the ejector device3.

The control unit 60 is connected to the expansion device 5 and comprisesmeans for transmitting control information to the expansion device 5 foradjusting the flow of the heat transfer medium through the expansiondevice 5 so that the heat transfer medium is mainly in the gaseous stateafter passing the secondary first heat exchanger 6.

In FIG. 2 the external circuit 14 runs through the primary 7 andsecondary 6 first heat exchangers in series, thus cooling the furtherheat transfer medium in two steps. The two first heat exchangers 6,7 mayalternatively cool two separate further heat transfer mediums inparallel.

FIG. 3 shows a diagram of a heat transfer circuit 10 of the apparatus 50according to a further embodiment of the invention. The heat transfercircuit 10 in FIG. 3 differs from the heat transfer circuit 10 in FIG. 2in that the heat transfer circuit 10 additionally comprises an internalheat exchanger 8 in the heat dispatch path 12, and an additional pathwhich comprises a flow restriction 9 and connects the heat receipt path11 downstream of the separator 4 and upstream of the first heatexchangers 6,7 to the heat dispatch path 12 downstream of the separator4 and upstream of the compressor device 1. This heat transfer circuit 10is especially beneficial if the compressor device 1 is lubricated bylubricating oil, which may exit said compressor device 1 and enter theseparator 4, where it may be mixed into the liquid part 42 of the heattransfer medium. The flow restriction 9 is included to bleed a smallamount of liquid heat transfer medium including lubricating oil into theheat dispatch path 12 to return the oil to the compressor device 1. Theinternal heat exchanger 8 ensures that all the liquid heat transfermedium vaporises before entering the compressor device 1 and that theheat transfer medium is not too cold for optimal functioning of thecompressor device 1.

FIG. 4 shows a diagram of a heat transfer circuit 10 of the apparatus 50according to an even further embodiment of the invention. Thisembodiment is similar to the embodiment shown in FIG. 2, but in theembodiment shown in FIG. 4 the primary first heat exchanger 7 isarranged in the separator 4 instead of the in a primary heat receiptpath 11 a (as shown in FIG. 2). The arrangement shown in FIG. 4 providesa similar technical effect as the arrangement shown in FIG. 2. At lowcooling need when the compressor 1 runs at low capacity, no heattransfer medium will be conducted through the secondary heat receiptpath 11 b, as the flow through the ejector 3 is too low to create asuction pressure at the suction inlet 32. However, as the primary firstheat exchanger 7 is positioned in the separator 4, heat will still betransferred to the heat transfer medium in the separator 4. This willcause some of the heat transfer medium in the liquid phase to vaporiseto the gaseous phase, which will be available for the compressor 1 viathe heat dispatch path 12. The heat transfer circuit 10 of the inventiontherefore avoids the problems of the prior art embodiment which mayarise at low cooling requirement. When the cooling requirement increasesand the compressor 1 runs with higher capacity, a suction pressure atthe suction inlet 32 of the ejector 3 is established, and flow of theheat transfer medium through the secondary receipt path 11 b will beestablished.

The invention also relates to a method of controlling the apparatus 50.The method comprises an initial step of receiving information from thesensor 62 for identifying a state of the heat transfer medium downstreamof the secondary first heat exchanger 6 and upstream of the suctioninlet 32 of the ejector device 3.

In a subsequent step the method comprises adjusting the flow of the heattransfer medium through the expansion device 5 on the basis of theinformation from the sensor 62 so that the heat transfer medium ismainly in the gaseous state after passing the secondary first heatexchanger 6. Thereby, it is assured that the suction inlet of theejector device 3 receives the heat transfer medium mainly in the gaseousstate.

Preferably, the flow of the heat transfer medium is adjusted so thatmore than 90% of the heat transfer medium is in the gaseous state, morepreferably more than 95% of the heat transfer medium.

It should be noted that the above-mentioned embodiments illustraterather than limit the invention, and that those skilled in the art willbe able to design many alternative embodiments without departing fromthe scope of the appended claims. Use of the verb “comprise” and itsconjugations does not exclude the presence of elements or steps whichare not stated in a claim. The article “a” or “an” preceding an elementdoes not exclude the presence of a plurality of such elements.

1. An apparatus for transferring heat, the apparatus comprising a heattransfer circuit with a heat transfer medium, wherein the heat transfercircuit comprises: a heat receipt path comprising a first heat exchangerfor transferring heat to the heat transfer medium; a heat dispatch pathcomprising a compressor device and a second heat exchanger fortransferring heat away from the heat transfer medium; and anintermediate path between the receipt path and the dispatch path, whichintermediate path comprises an ejector device and a separator, whereinthe ejector device comprises a main inlet connected to the dispatchpath, a suction inlet, and main outlet connected to the separator, andwherein the separator is configured to receive heat transfer medium fromthe ejector device and to provide heat transfer medium to the heatreceipt path and the heat dispatch path, wherein the first heatexchanger comprises a primary first heat exchanger and a secondary firstheat exchanger, wherein a) the heat receipt path further comprises aprimary heat receipt path arranged with the primary first heat exchangerand connected to the separator without passing the ejector device, or b)the primary first heat exchanger is arranged in or in direct connectionto the separator, wherein for both options a) and b) the heat receiptpath further comprises a secondary heat receipt path arranged with thesecondary first heat exchanger connected to the suction inlet of theejector device, wherein the secondary heat receipt path furthercomprises an expansion device upstream of the secondary first heatex-changer.
 2. The apparatus according to claim 1, wherein the heattransfer medium mainly comprises CO2.
 3. The apparatus according toclaim 1, wherein the apparatus comprises at least one sensor foridentifying a physical quantity dependent on a state of the heattransfer medium and a control unit, wherein the at least one sensor ispositioned downstream of the secondary first heat exchanger and upstreamof the suction inlet of the ejector device, and the control unit isadapted to receive information from the at least one sensor and controlthe expansion device on the basis of said information so that the heattransfer medium is mainly in the gaseous state after passing thesecondary first heat exchanger.
 4. The apparatus according to claim 3,wherein the sensor is one of a temperature sensor, a pressure sensor andan optic sensor.
 5. The apparatus according to claim 1, wherein theprimary first heat exchanger is positioned lower in elevation than theseparator.
 6. The apparatus according to claim 1, wherein the primaryheat receipt path further comprises a pump device for conducting theheat transfer medium through the primary first heat exchanger.
 7. Theapparatus according to claim 1, wherein the heat dispatch path comprisesan internal heat exchanger for exchanging heat between the heat transfermedium flowing upstream of the compressor device and downstream of thesecond heat exchanger.
 8. The apparatus according to claim 1, whereinthe apparatus comprises an additional path connecting the heat receiptpath downstream of the separator and upstream of the first heatexchanger to the heat dispatch path downstream of the separator andupstream of the compressor device, wherein the additional path comprisesa flow restriction.
 9. A method for transferring heat via an apparatus,the apparatus comprising a heat transfer circuit with a heat transfermedium, wherein the heat transfer circuit comprises: a heat receipt pathcomprising a first heat exchanger for transferring heat to the heattransfer medium; a heat dispatch path comprising a compressor device anda second heat exchanger for transferring heat away from the heattransfer medium; and an intermediate path between the receipt path andthe dispatch path, which intermediate path comprises an ejector deviceand a separator, wherein the ejector device comprises a main inletconnected to the dispatch path, a suction inlet, and main outletconnected to the separator, and wherein the separator is configured toreceive heat transfer medium from the ejector device and to provide heattransfer medium to the heat receipt path and the heat dispatch path,wherein the first heat exchanger comprises a primary first heatexchanger and a secondary first heat exchanger, wherein a) the heatreceipt path further comprises a primary heat receipt path arranged withthe primary first heat exchanger and connected to the separator withoutpassing the ejector device, or b) the primary first heat exchanger isarranged in or in direct connection to the separator, wherein for bothoptions a) and b) the heat receipt path further comprises a secondaryheat receipt path arranged with the secondary first heat exchangerconnected to the suction inlet of the ejector device, wherein thesecondary heat receipt path further comprises an expansion deviceupstream of the secondary first heat ex-changer, wherein the methodcomprises the steps of: receiving information from at least one sensorfor identifying a state of the heat transfer medium downstream of thesecondary first heat exchanger and upstream of the suction inlet of theejector device, and adjusting the flow of the heat transfer mediumthrough the expansion device on the basis of the information from the atleast one sensor so that the heat transfer medium is mainly in thegaseous state after passing the secondary first heat exchanger. 10.(canceled)